Production of 2-hydroxyacetylfuran from lignocellulosics treated with ionic liquid-water mixtures

Article abstract of DOI:10.1039/c5ra14205a

Japanese cedar (Cryptomeria japonica) was treated with 12 ionic liquid (IL)-water mixtures at 120 °C for 1 h. Production of 5-hydroxymethylfurfural, furfural and 2-hydroxyacetylfuran (2-HAF) was observed by HPLC and GC-MS. This is the first report to identify 2-HAF from lignocellulosics using ILs. The optimal IL-water mixture was found to be a 90% pyridinium chloride and 10% water w/w solution, although any IL-water mixture that contained pyridinium or imidazolium salts produced all three compounds in varying yields.

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Production of 2ꢀhydroxyacetylfuran from lignocellulosics treated with ionic
liquidꢀwater mixtures
a
Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, Hangiꢀcho,
Shimogamo, Sakyoꢀku, Kyoto 606ꢀ8522, Japan.
b
Department of Biomass Chemistry, Forestry and Forest Products Research Institute, Matsunosato 1,
Tsukuba, Ibaraki 305ꢀ8687, Japan.
c
Functional Ionic Liquid Laboratories, Graduate School of Engineering, Tokyo University of Agriculture
and Technology, 2ꢀ24ꢀ16 Nakaꢀcho, Koganei, Tokyo 184ꢀ8588, Japan.
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a
Koichi Yoshioka, Tatsuhiko Yamada, Hiroyuki Ohno, Hisashi Miyafuji *
*Corresponding author
Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, Hangiꢀcho,
Shimogamo, Sakyoꢀku, Kyoto 606ꢀ8522, Japan.
TEL: +81ꢀ75ꢀ703ꢀ5646, FAX: +81ꢀ75ꢀ703ꢀ5646
Eꢀmail: miyafuji@kpu.ac.jp
Keywords: ionic liquid; 2ꢀhydroxyacetylfuran; lignocellulosics; pyridinium chloride; furan; cellulose;
hemicellulose; Cryptomeria japonica; biorefinery
1

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Abstract
Japanese cedar (Cryptomeria japonica) was treated with 12 ionic liquid (IL)–water mixtures at 120°C for 1
h. Production of 5ꢀhydroxymethylfurfural, furfural and 2ꢀhydroxyacetylfuran (2ꢀHAF) were observed by
HPLC and GCꢀMS. This is the first report to identify 2ꢀHAF from lignocellulosics using ILs. The optimal
IL–water mixture was found to be a 90% pyridinium chloride and 10% water w/w solution, although any IL–
water mixture that contained pyridinium or imidazolium salts produced all three compounds in varying
yields.
1. Introduction
Lignocelluloses are the most abundant renewable resource on the planet and are mainly comprised of three
biopolymers: cellulose, hemicellulose and lignin. Recently, they have attracted attention as viable alternative
renewable carbon resources to fossil fuels. Cellulose, which has a βꢀ1,4ꢀglucan chemical structure, and
1
hemicellulose, which is mainly composed of hexoses and pentoses, can be converted to biofuels and various
2
raw materials (Fig. 1) via chemical and biological reactions. Lignin is an aromatic biopolymer
biosynthesized from phenylpropane via oxidative radical coupling, which can be transformed to significant
3
aromatic building blocks of chemicals.
4
After the United States Department of Energy established 12 chemical building blocks in 2004, research
into the production of useful compounds and materials from carbohydrates in lignocellulosics has increased
significantly. 5ꢀHydroxymethylfurfural (5ꢀHMF), which can be synthesized from fructose and glucose, is a
key intermediate and can be transformed into any one of the twelve chemical building blocks.
2,5ꢀFurandicarboxylic acid, which is a candidate fuel source and a raw material in the production of plastics,
can be prepared by oxidation of 5ꢀHMF. Levulinic acid (Fig. 1), which is also one of the 12 building blocks,
5
can be obtained from 5ꢀHMF by hydrolysis reactions under acidic conditions.
Swatloski et al. have reported that ionic liquids (ILs), which are organic salts with melting points below
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around 100°C, can dissolve cellulose. Subsequently, studies on the treatment of lignocellulosics with ILs
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,8
has been increasing. The reaction behaviors of cellulose and wood with imidazolium or pyridiniumꢀbased
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ILs have been investigated and a morphological study of wood with ILs has been published.
Many groups have attempted to convert lignocellulosics, or lignocellulosicsꢀrelated compounds, into useful
compounds using different ILs. Saccharides (e.g., glucose, fructose and cellulose) with different ILs have
11ꢀ16
been used mainly as starting materials in the production of 5ꢀHMF.
In some examples, 5ꢀHMF could be
2

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produced from the saccharides with the use of a catalyst.
There have been few studies, however,
examining the production of lignocellulosics from wood, and all of these have used ILs with lower volumes
of water and dried samples. Application of IL–water systems for the treatment of lignocellulosics provides
several advantages over other methods.
First, the drying of lignocellulosics is often required because they contain water, but if an IL–water method is
used, then this drying step can be removed from the production process. Second, the solidꢀstate ILs at
ambient temperature and dissolved in water can behave as solvents for the biorefinery of lignocellulosics.
Thereby, many different IL–water solvent systems can be used for the treatment of lignocellulosics. Third,
the addition of water to IL reduces the financial cost and the potential environmental impact because the total
volume of ILs that is needed can be reduced. Recently, Abe et al. reported tetraꢀnꢀbutylammonium hydroxide
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and tetraꢀnꢀphosphonium hydroxide that contained water successfully dissolved wood at room temperature,
and solutions of ILs and acids were employed as pretreatments in the production of bioethanol via
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saccharification.
Although IL−water mixtures are attractive solvent systems, and have great potential for the conversion of
lignocellulosics to valuable compounds, studies on the treatment for lignocellulosics with IL–water mixtures
have not been undertaken in detail. In this paper, we report the analysis of the soluble fractions obtained from
Cryptomeria japonica treated with IL–water mixtures, without catalysts, and describe the identification of
2ꢀHAF from the sample.
2. Experimental
2.1 Materials
All solvents were of analytical grade and purchased from Wako Pure Chemical Industries Ltd (Osaka,
Japan) or SigmaꢀAldrich (St. Louis, MO). Ionic liquids and authentic samples of furan compounds were
purchased from Tokyo Chemical Industry Co., Ltd (Tokyo, Japan), Wako Pure Chemical Industries Ltd. or
SigmaꢀAldrich (St. Louis, MO). Chloroformꢀd was purchased from Cambridge Isotope Laboratories Inc.
(Andover, MA). MilliꢀQ water was used for IL treatments and HPLC analysis. C. japonica (Japanese cedar)
was ground in a Wileyꢀmill to a particle size between 90 and 180 µm and then successively extracted with
ethanol/benzene (1/2, v/v) for 6 h in a Soxhlet extractor to remove several extractives in C. japonica. The
extracted wood powders were dried in an oven at 105 °C for 24 h prior to further processing (see section
2.4).
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2.2 Instruments
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H NMR spectra were recorded on a Bruker AVANCE400 operating at 400 MHz. Chemical shifts (δ) are
(δ 7.26 ppm) as internal standards. Mass
given in ppm relative to tetramethylsilane (δ 0.00 ppm) or CHCl
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spectra were obtained on a Shimadzu GCꢀMS (Shimadzu Co., Ltd, Kyoto, Japan) equipped with a DBꢀ5MS
column (30 m × 0.25 mm i.d., 0.25 ꢁm film thickness, Agilent Technologies, USA). Analytical thinꢀlayer
chromatography (TLC) was performed on Merck preꢀcoated silica gel plates (Kiesel gel 60F254 plate, 0.25
mm thick; Merck, USA) and silica gel column chromatography was carried out on a Kanto Chemical silica
gel 60N (spherical, neutral, 63–210 µm). HPLC separation was conducted on a Shimadzu Prominence
(Shimadzu Co., Ltd, Kyoto, Japan) equipped with an LCꢀ20AD pump, a CTOꢀ20A column oven, and an
SPDꢀM20A photodiode array. The HPLC conditions were: Aminex HPXꢀ87H column (BioꢀRad
2 4
Laboratories, Inc., Hercules, CA), a flow rate of 0.6 mL/min, 5 mM H SO as the mobile phase using a
column temperature of 45 °C, and sample detection via UV absorbance at 280 nm.
2.3 Preparation of authentic 2ꢀhydroxyacetylfuran (2ꢀHAF)
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2ꢀHAF was prepared as previously conducted in the paper. Sucrose (30 g) and oxalic acid (0.3 g) were
dissolved in 100 mL of water. The solution was heated at 140°C in an autoclave for 3 h. After cooling to
room temperature, the reaction mixture was neutralized with saturated NaHCO
µm membrane filter. The filtrate was evaporated and then extracted with ethyl acetate four times before the
combined organic layers were washed with water and dried over Na SO . Finally, the crude sample was
3
aq. and filtered with 0.45
2
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obtained after drying in vacuo at room temperature then purified by flash chromatography on a silica gel
(ethyl acetate : hexane = 1:2, v/v) to give 2ꢀHAF (30 mg) in 0.1% yield. The identity of 2ꢀHAF was
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established by H NMR and GCꢀMS. Spectra data of 2ꢀHAF: H NMR (400 MHz, CDCl ) δ 3.26 (1H, t, J =
4.4 Hz), 4.75 (2H, d, J = 4.4 Hz), 6.60 (1H, dd, J = 1.6, 3.6 Hz) 7.31(1H, dd, J = 0.8, 3.6 Hz), 7.64 (1H, dd, J
+
= 0.8, 1.6 Hz), GCꢀMS m/z 126 [M] , 95, 67, 51, calculated mass of C
6 6 3
H O is 126.03.
2.4 Treatment of C. japonica with ionic liquid−water mixtures
Typical experiments using ionic liquids are shown in Table 1. Airꢀdried wood powders from section 2.1
(0.18 g), ionic liquids (3.0 g), and MilliꢀQ water (0.33 g) were added to a 15ꢀmL ace glass pressure tube (Ace
glass, Inc., Vuneland, NJ). For entry 3, airꢀdried cedar powder (0.12 g), 1ꢀethylpyridinium chloride (2.0 g),
and MilliꢀQ water (0.22 g) were added to a glass tube. For entry 8, airꢀdried cedar powder (0.18 g), and
pyridinium chloride ([Py][Cl], 3.0 g) were added to a 15ꢀmL glass tube and the mixture was stirred for 20
min at 160°C in an oil bath. For entry 13, airꢀdried cedar powder (0.18 g) was added to 2.78 mL of a 1.5%
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v/v hydrochloric acid solution in a 15ꢀmL glass tube. The mixtures were stirred for 1 h at 120°C in an oil
bath. After each reaction, 50 µL of each solution was taken and diluted with 450 µL of water. The solutions
were shaken and filtered through a 0.45ꢀµm syringe filter. The filtrate (10 µL) was then analyzed by HPLC.
The reaction solutions using imidazolium chloride (entry 4), hydrazinium chloride (entry 7) and pyridinium
chloride (entry 8) were diluted with water in order to take them easily.
Airꢀdried wood powder (0.36 g), [Py][Cl] (6.0 g) and MilliꢀQ water (0.66 g) were added to a 35ꢀmL ace
glass pressure tube (Ace glass, Inc., Vuneland, NJ). The residual reaction solution was filtered through a
glass filter with 1 µm of pore size and the filtrate was evaporated. Next, the reduced filtrate was dried in
vacuo at room temperature and the dark colored residue obtained was extracted with acetone. Finally, the
acetone extract was filtered through a 0.45ꢀµm syringe filter before it was analyzed by GCꢀMS.
3. Results and discussion
2
0ꢀ23
We first chose [Py][Cl] for our IL−water mixtures because of its success in previous studies.
The HPLC
chromatogram of the soluble fraction obtained from C. japonica treated with a [Py][Cl]–water mixture at
120°C for 1 h is shown in Fig. 2. By comparison with authentic samples, the compounds corresponding to
the peaks at 31 min (peak 1) and 47 min (peak 3) were identified as 5ꢀHMF and furfural, respectively;
however, the peaks at 21, 23, 34 and 44 min in the chromatogram could not be immediately identified.
Structure elucidation of the unknown compound for the distinctive peak at 34 min was investigated. Using
UV absorbance and HPLC retention time, we hypothesized that the compound had a furan skeleton.
Moreau et al. have proposed conversion routes of monosaccharides to furan compounds such as furfural,
24,25
5ꢀHMF and 2ꢀHAF (Fig. 1).
Their results show that the three different furan compounds can be formed
via a 1,2ꢀenediol intermediate from monosaccharides by the acyclic route. They demonstrated that furfural
and 5ꢀHMF were produced from fructose by dehydration, but extraction of 2ꢀHAF in the mixture was not
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observed. However, volatile compounds, including 2ꢀHAF, have been observed in foods
and other
using GCꢀMS. A trace amount of 2ꢀHAF was detected in the acid catalyzed dehydration of
fructose, and conversion of cellulose to 2ꢀHAF was demonstrated in a concentrated zinc chloride solution
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materials
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under microwave irradiation at 135°C.
Glucose and mannose, which can be converted to fructose by
isomerization, are in high concentration in lignocellulosics, even though production of 2ꢀHAF from
lingocellulosics with IL has not been reported as far as we know.
Given this, we assumed that 2ꢀHAF could be obtained from lignocellulosics and further analysis of the
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soluble fraction from C. japonica was attempted. Unfortunately, an authentic sample of 2ꢀHAF is not
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available commercially so we prepared an authentic sample of 2ꢀHAF by the degradation of sucrose. The
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authentic 2ꢀHAF was characterized by H NMR and GCꢀMS, and gave an HPLC retention time of 34 min.
The results therefore indicate that the unidentified peak 2 in Fig. 2 was 2ꢀHAF. Additionally, the acetone
extract from the soluble fraction of C. japonica treated with [Py][Cl]−water at 120°C for 1 h was subjected
to GCꢀMS. A peak at 9 minutes showed a mass spectrum with a molecular ion at m/z 126 and fragment ions
at m/z 95, 67 and 51. The fragmentation pattern of the peak was the same as authentic 2ꢀHAF. Therefore, we
conclude that the compound corresponding to the peak at 34 min was 2ꢀHAF.
Samples of C. japonica were also treated with other IL–water mixtures and quantitative analysis of the furan
compounds in each soluble fraction was undertaken (Table 1). For entry 8, C. japonica was treated with
[Py][Cl] at 160°C without the addition of water because its melting point is around 144−148°C. 5ꢀHMF and
furfural were successfully formed in the soluble fractions obtained from C. japonica treated with different
IL–water mixtures, except for the ILs that contained hydrazinium chloride, guanidinium chloride and
piperidinium chloride–water mixtures (Entries 7, 10 and 12).
Production of 2ꢀHAF from lignocellulosics depends on the ILs as 1.5% v/v hydrochloric acid was not a
suitable solvent for producing 2ꢀHAF (Entry 13). Overall the results indicate that it is likely that pyridinium
and imidazolium play an important role in the production of 2ꢀHAF from saccharides in lignocellulosics.
Consequently, it was found that a 90% [Py][Cl] and 10 % w/w water solution is the most effective for the
production of 2ꢀHAF from C. japonica (Entry 1).
There are two stages in the reaction to produce furan compounds from polysaccharides in lingocellulosics.
First stage is hydrolysis of polysaccharides to produce various monosaccharides. Second stage is the
conversion of the obtained monosaccharides into furan compounds by dehydrations as described in the
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previous paper.
10 % of water in [Py][Cl] seems to be appropriate ratio for the production of
monosaccharides. The role of water at the second stage, however, has not been clarified as far as we know.
Because acidity of pyridinium chloride is stronger than that of imidazolium chloride in water, pyridinium
chloride is thought to promote the hydrolysis of polysaccharides in the first stage. Thus, the yields of 5ꢀHMF
and 2ꢀHAF in the reaction with pyridinium chloride were superior to those with imidazolium chloride since
monosaccharides, the precursors of furan compounds, are rich in the reaction media with pyridinium
chloride.
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We are presently investigating the reaction behavior of lignocellulosics with [Py][Cl]–water mixtures and the
formation mechanism of 2ꢀHAF using model compounds related to lignocellulosics.
4. Conclusions
We have demonstrated that the treatment of C. japonica with different IL–water mixtures produces furfural,
5ꢀHMF and 2ꢀHAF with yields dependent on which organic compounds are used in the IL–water mixtures.
This paper is the first report to identify 2ꢀHAF in the reaction mixtures obtained from woody biomass using
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ILs indicating that 2ꢀHAF has potential as a new platform
in lignocellulosic biorefinery.
Acknowledgements
The authors wish to thank Ms Chihiro Kohsaka of the Kyoto Municipal Institute of Industrial Technology
and Culture for her assistance with GCꢀMS and Mr. Ryoya Ito for great help with the preparation of 2ꢀHAF.
This work was supported by a Science and Technology Research Promotion Program for Agriculture,
Forestry, Fisheries and Food Industry grant (No. 26052A) from the Ministry of Agriculture, Forestry and
Fisheries of Japan.
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40 B. M. Trost, H. Ito and E. R. Silcoff, J. Am. Chem. Soc., 2001, 123, 3367–3368.
41 B. M. Trost and V. S. C. Yeh, Org. Lett., 2002, 1, 3513–3516.
Figures and Tables
Fig. 1 Chemical structures of furan compounds derived from polysaccharides in lignocellulosics.
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Page 10 of 11
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DOI: 10.1039/C5RA14205A
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
Fig. 2 HPLC chromatogram of the soluble fraction obtained from C. japonica treated with a 90%/10% w/w
solution of [Py][Cl] and water. Peaks 1, 2 and 3 were identified as 5ꢀHMF, 2ꢀHAF and furfural, respectively.
Table 1. Furan yields from C. japonica after treatment with different ILꢀwater mixtures.
Water
5
ꢀHMF
2ꢀHAF
Furfural
Entry
Ionic liquids
content
a
a
a
(
wt%)
(wt%)
(wt%)
(
wt%)
1
2
3
4
5
6
7
8
9
Pyridinium chloride
Pyridinium pꢀtoluenesulfonate
1ꢀEthylpyridinium chloride
Imidazolium chloride
10
10
10
10
10
10
10
0
2.96
0.69
2.79
0.48
0.69
1.56
3.40
trace
1.28
0.16
0.29
0.40
1.45
0.86
0.59
1.14
1.11
1.87
1ꢀMethylimidazolium chloride
1ꢀMethylimidazolium hydrogen sulfate
Hydrazinium chloride
b
b
b
n.d.
n.d.
n.d.
Pyridinium chloride
0.59
1.50
0.48
0.88
0.18
0.94
Pyridinium chloride
20
20
30
30
b
b
b
10
11
12
13
Guanidinium chloride
n.d.
n.d.
n.d.
Pyridinium bromide
0.72
0.19
0.57
b
b
b
Piperidinium chloride
n.d.
n.d.
n.d.
b
1.5% v/v Hydrochloric acid
ー
0.29
n.d.
0.48
a
b
314
per dry wood, not detected
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2
-Hydroxyacetylfuran, which has potential as a new platform, was firstly identified in
wood treated with ionic liquid-water mixtures.